This invention relates to surface planing or submerged watercraft such as surfboards, kiteboards, sailboats, submersible craft, etc. and specifically to fins or keels of which the primary function of fins or keels attached to a watercraft surface that contacts water is to provide dimensional stability and control of watercraft while moving or propelled through water either on water surface or submerged. The present invention improves on existing designs by providing an increased area of lateral flex (leading edge to trailing edge), and a reduction of fin or keel volume by modification to fin or keels cross sectional profile which is not featured in existing designs. The number, shape, size, and location of fins or keels is dependent on the desired function and performance of said watercraft. For example, as a watercraft moves through water in a forward direction the water flow and water pressure or hydrodynamic pressure are equal on either side of a fin or keel. As direction of watercraft changes (i.e. Turning or tacking) water pressure or hydrodynamic pressure increases on the turns inner radius side of fin or keel and decreases on the turns outer radius side of fin or keel surface. When the water pressure or hydrodynamic pressure becomes too great on the inner radius side of fin or keel and too deficient on the outer radius side of fin or keel the low pressure side produces a low pressure core in the laminar flow boundary resulting in cavitating flow. At the point when a fin or keel produces cavitating flow the fin or keel loses the ability to provide dimensional stability resulting in the loss of control of watercraft by operator. The invention as presented provides several novel improvements over current or traditional fin or keel designs.
Borrowing from the natural design of the fins of fish and cetaceans also known as biomimicry, the invention as presented increases efficiency and improves performance of fins or keels by reducing cavitating flow during directional changes by allowing the rear portion of fin or keel to react by flexing laterally in proportion to increasing water pressure on fin or keel surface experienced while turning or tacking of said watercraft. The invention as presented provides novel improvements over conventional cross sectional fin or keel profiles by reducing the total volume of fin or keel by orientating the greater volume of fin or keel to the leading edge portion of said fin or keel and decreasing the volume of said fin or keels trailing edge portion. There are several patents directed toward fins or keels featuring a lateral flex component employed for dimensional stability and control of surface planing or submerged watercraft. These devices are limited in their functionality by the degree of lateral flex, the distribution of lateral flex area, total volume of fin or keel and the cross sectional profile of fin or keel.
Lewis, U.S. Pat. No. 5,480,331 discloses a flexible fin for surfboards comprised of a fiberglass core sandwiched between two closed cell polyurethane foam surface layers.
Skedeleski/Arakawa, U.S. Pat. No. 5,306,188 discloses a surfboard fin consisting of a rigid body element with a soft flexible material covering the leading and trailing edges of fin. The soft flexible leading edge and the soft flexible trailing edge reduces injury from impact of fin to surfer and provides a rudder action by flexing during turns.
Additional advantages are an increase in watercraft speed by reducing turbulence of laminar flow exiting fins or keels and reduction of fin or keel weight by reduction of fin or keel volume. Additional advantages, objects, and novel features will become apparent when reviewing the detailed description and claims in conjunction with the detailed drawings.